Determination of Organic Substances bY Standard Chromous Chloride Solution Nitroso Compounds N. HOWELL FURMAN and RUDOLPH S. BOTTEI' Department o f Chemisfry, Princeton Universify, Princeton, N. 1.
F A standard chromous chloride solution, prepared determinately from potassium dichromate, was used for the determination of p-nitrosodimethylaniline, the ammonium salt of N-nitrosophenylhydroxylamine (cupferron), Nnitrosodiphenylamine, and N-nitrosoN-phenylbenzylamine. The compounds were treated with an excess of the reducing agent at room temperature, and the excess was determined with standard ferric alum solution. The end point of the titration was determined potentiometrically. Because of the instability of cupferron, N-nitrosodiphenylamine, and N-nitroso-N-phenylbenzylamine in acid solution, special procedures were used for their determination. p-Nitrosodimethylaniline, N-nitrosodiphenylamine, and N-nitroso-N-phenylbenzylamine were reduced to the corresponding amines; in cupferron, there was a reductive cleavage of the nitroso group with the formation of phenylhydroxylamine and ammonia.
T
CHLORIDE has been used by a number of investigators to determine p - nitrosodimethylaniline. Iinecht and Hibbert (7) titrated directly in acid medium a t 40' to 50' C., while Dachselt (4) did a direct titration using the alkaline buffer method of Kolthoff and Robinson (8). Salraterra (12) added a n excess of reagent, boiled, and titrated the excess n-ith methylene blue. l l u s h a (11) determined nitroso compounds using titanous sulfate, prepared by reducing titanium(1V) sulfate x i t h zinc amalgam. H e also reduced a nitroso compound with a liquid amalgam and determined the reduced product photometrically by diazotization (10). Gapachenko (6) reduced cupferron to the corresponding amine b y adding a n excess of trivalent molybdenum and back-titrated the excess with ferric alum, using methylene blue as a n indicator. i i n iodometric procedure (1, 91 based on the quantitative oxidation of iodide by the nitroso group has been del-eloped for the determination of .V-nitrosodiphenylamine. Kitroso com-
ITASOUS
Present address, Department of Chemistry, University of S o t r e Dame, S o t r e L):ime, Inrl.
pounds may be determined by the Iijeldah1 method (3, 5 ) ; however, it is first necessary to reduce the nitroso nitrogen to t h e amine to prevent loss of nitrogen. I n a previous publication ( 2 ) , the analysis of nitroso R salt using standard chromous chloride was reported. Recently, the method was applied to p nitrosodimethylamine, the ammonium salt of S-nitrosophenylhydroxylamine (cupferron) , S - nitrosodiphenylamine, and S-nitroso-Ar-phenylbenzy1amine to establish whether the method is generally suited for the determination of the other types of nitroso compounds.
EXPERIMENTAL
about a minute before being backtitrated n-ith standard ferric aluni solution. CUPFCRROS.A mixture of 30 inl. of distilled water and 10 ml. of concciitrated hydrochloric acid was deaerated for about 10 minutes by bubbling oxygen-free carbon dioxide through the solution. A t the end of this period, t h e carbon dioxide was passed over the surface of the solution. Chromous chloride was then allowed to run into t h e hydrochloric acid solution, and the sample introduced after about 15 nil. of chromous chloride had been added. The reaction mixture was allowed t o stand for a minute before being backtitrated \\ith ferric alum. ~-SITROSODIPHEKYLAMIK AND *Y~ I T R O 5 O - i ~ - P H E h - Y L B E K Z Y L S h l I S E . The solid samples were dissolved in 95% ethyl alcohol and deaerated with oxygen-free carbon dioxide for about 3 to 5 minutes. Then the carbon dioxide wits passed over the surface of the solution. Chromous chloride was then allowed to run into the solution, and after about 15 ml. had been added, 10 nil. of concentrated hydrorhloric acid (previously deaerated) n as introduced into the ieaction mixture. After the required P Y C ~ S S of chiomous was added, the ieaction rnistuie n as allon-ed to stand foi a miiiute befoie haclk titration. Blanks employing the same s o l r m t conditions and same ixoeedurc as for
Apparatus. The apparatus used for storing and dispensing standard chromous chloride, the titration cell, and the means of determining the end point of the titration have been described ( 2 ) . Reagents. Standard solutions of chromous chloride and of ferric alum n-ere prepared (8). Samples. Eastman Ilodak Co. cupferron was twice recrystallized from nbsolute ethyl alcohol, dried in air, and stored in a dark bottle containing a bag of ammonium carbonate. ii standard solution was prepared b y dissolving a k n o m amount in 500 ml. of distilled n-ater. Samples of p-nitrosodimethylaniline were prepared by weighing out to the nearest 0.1 mg. various amounts of p nitrosodimethylaniline (hlatheson, Coleman, and Bell Co.) into tall-form Table I. Determination of electrolytic beakers. p-Nitrosodimethylaniline Eastman Kodak Co. S-nitrosodiphenylamine and N-nitroso-*V-phenylExcess Chromous benzylamine were twice recrystallized Tdkcn, Chloiide, Found, E i ~ r o t , from absolute ethyl alcohol and dried in Jlg. 70 Mg. 70 air. Samples were prepared by weighing out to the nearest 0.1 mg. various 111,o 25 138.1 - 2 . 1 amounts of t h e compound into tall-form 131.7 20 130.4 -1 0 electrolytic beakers. .-i0 101.6 -2 (i 101. :3 12 84.4 -2.0 Procedures. ~NITROSODIMETHYLANI- SA. 1 LIXE. The samples m-ere dissolved in 40 72 2 160 71 1 -1 5 nil. of glacial acetic acid and 10 ml. of -1 3 100 G8 7 69 6 concentrated hydrochloric acid was -1 0 (i8.9 I50 A8 2 added to the solution. Carbon dioxide, -1 8 67 0 100 65 8 freed from traces of oxygen b y passage 59 2 150 58 7 -0 85 -1 3 58 6 100 57 8 through a n acidified solution of chromous chloride in contact with anialga-1.7 68 2 50 67 2 mated zinc, was bubbled through the 49 I -0 11 10 3 200 solution for about 10 minutes. Then, the 46 5 -1 7 17.3 260 carbon dioxide was passed over surface -1 3 250 46 0 46.6 -1 3 260 of t h e solution. An excess of 0.1000-V 37 9 38 4 -0 41 500 24 3 24 4 chromous chloride was added and the reaction mixture was allowed to stand VOL. 29, NO. 1, JANUARY 1957
121
Table II.
Taken, hieq. 1 000
0 500
Determination of Cupferron
Excess Chromous Chloride,
%
200 200 200 300 300 300 300 300 400 400 500 500 GO0
Found, hleq. 0 981 0 984 0 987 0 997 1 000 1 000 1 002 1 004 0 481 0 491 0 499 0 500 0 501
Error,
%
-1 -1 -1 -0
0 0 +0 +0 -1 -1 -0 0 +0
9
G
3 30 0 0 20 40 8 8 20 0 20
Table 111. Determination of N-Nitrosodiphenylamine
Taken, 3Ig. 160 6 120 6
119 5 114 G D i G 75 4 74 4 i0 9
Gi 7 63 4
59 i 58 3 56 G 5-1- 3 54 0 52 1 50 1
Excess Chromous Chloride,
Found,
% 50 25 100 50 175
200 100 200 250 250 250 300 300 350 250 350 350
wz.
161 118 120 114
7 8
Error,
% +0 56 -1 5 76
7G 1 75 2 il 5 69 2 63 6 (io 2 59 1
+0 -0 $0 t 0 +1 +0 +2 +0 +0 $1
57 i
$1
4 3
80 3
543 55 3 52 4 51 0
Table IV. Determination of N-Nitroso-N-phenylbenzylamine
0 +2 +0
2b 88
93
1 85
2 32 84 4 9 0 2 57
Taken, ?\lg 229 G
118 115 100 95 92
1 2 0 G 0
88 5 78 G 76 9 75 9
71 71 68 65 65 64 63 57 54 54
9 6 0 7 3 0 2 2 9 1 50 3 46 4 42 2 40 3 37 3 36 7 34 1 32 0 27 G
Excess Chromous Chloride,
%
IO
100 100 150 150 150 150 200 100 200 230 200 250 1 .io
360
250 300 300
100 200 200 300 400 400 350 150 500 400
200
Found,
Error,
117 G 112.4 100 7 95 2 91.1
-0.42 -2.4 +0.i -0.42 -0.98 -0.91 1 0 . I3 -1.2
Rlg. % 223 9 -2.5 ~~.
87.7 78.7
76.0 77 1 72 3 71 9 67 G A4 5. .~
GG 63 63 5i 54 53 51 4G 42 41
-1-
8
2 8 3 0
8
9 8
8
37 7 35 7
34 6 32 8 28 2
+I .G
+0.5G $0.42 -0.59 -1.2 il.7
-0.31 0.0
$1.1
-1.1 -0.37 +2.0 +1.1 +1.4 +2.4 1
+;. -
1
+l.5 +2.5 +2.2
+ S H J + H2O
H
DISCUSSION
The nitroso group in p-nitrosodimethylaniline, iY - nitrosodiphenylamine, and S-nitroso-Ar-phenylbenzylamine was reduced to the corresponding amino group-that is, four equivalents of chromous chloride were required per mole of compound. I n the case of cupferron, six equivalents were required per mole, which indicates that 122
ANALYTICAL CHEMISTRY
LITERATURE CITED
W. W.,Shaeffer, IT-. E., “Determination of Kitro, Nitroso, and Sitrate Groups.” in “Organic Analys~s,”T’ol. 11, p-p. 95-6, Interscience Publishers, Len- York-London, 1954. (2) Bottri, R. S.,Furman, K. H., ASAL. GHEJI. 27. 1182 (1956) (3, Cs&os, Z . , Foder-Kenczler, E., Mayyar Chein. Folydoirat 48, 33-42 (1942); Chenz. Zentr. No. 1, 545-8 (1943). (4) Dachselt, E., 2. anal. Chern. 68, 40410 (1926). (5) Friedrich, A , , Kuhaas, E., Schnurch, R., Z . physiol. Chein. 216, €18-76 (1933). (6) Gapachenko, 31. V., Zacodskaya Lab. 10, 246-8 (1941). (7) Iinecht, E., Hibbert, E., “Xew Reduction Methods in Volumet’ric Analysis,” 1st ed., reissue with additions, pp. 28-9, Longmans, Green, London, 1918. ( 8 ) Kolthoff, I. M.,Robinson, C., IZec. trav. chim. 45, 1G9-iG (1926). (9j Lobounets, 11.Li., Gortin’lra, E. S . , I.‘nav. titat k‘zez>, Bull. SCL., Kec. chztn., s o . 4, 37-9 (1939). (10) hIusha, S . , J . Chenz. SOC.J a p a n 66, 38-9 (1945). (11) Zbld. 67, 49-52 (1946). (12) Salvaterra, H., Chern.-Ztg. 38, 90-1 (1914). (1) Becker,
I
The results obtained for the determination of p-nitrosodimethylaniline, cLipferron, .Y-nitrosodiphenylamine, and A\.- nitroso - .Y - phenyl - benzylamine are listed in Tables I to IV. It is readily seen that these compounds may be satisfactorily determined by using standard chromous chloride as a reducing agent.
One of the authors (R. S. R.)would like to thank Princeton University for financial aid in the form of the LeRoy Wiley McCay Advanced Fellowship in analytical chemistry (1954-55).
a reductive cleavage occurred a t the
SO CsH,--S--OSH,
RESULTS
ACKNOWLEDGMENT
iY=Y bond as follom :
+l 8
the samples were run on the chromous chloride for each set of determinations. The blanks ranged from 0.10 to 0.15 nil.
tained by using about a 100% excess. In the determination of S-nitrosodiphenylamine, as well as A--nitroso-Al-phenylbenzylamine, results are slightly high, especially viith small samples and large excesses of chromous ion. This may be due to a slight amount of overreduction-that is, there is a reductive cleavage a t the S-Sbond as in the case of cupferron. Hoxever, although the compounds were recrystallizcd twice from absolute ethyl alcohol, there still may be some slight trace of reducible impurity which could easily account for the slightly high results. Several attempts nere made to determine p-nitrosodimethylaniline by titrating directly a t room temperature and also a t elevated temperatures. The rate of reduction in the vicinity of the end point n a s slow, even a t elevated temperatures. It n-as therefore preferable to use the indirect method of analysis.
With trivalent molybdenum, Gapachenko (6) found that the nitroso group in cupferron was reduced to t h e corresponding amino group. This may be attributed to the lesser reducing power of trivalent molybdenum as compared with divalent chromium. When the samples of cupferron, S-nitrosodiphenylamine, and S-nitrosoA7-phenylbenzylamine were prepared in acid medium, in the same manner as for nitroso R salt ( 2 ) and p-nitrosodimethylaniline, the results were erratic and very low. Results from 10 to 40y0 below the theoretical value were obtained, depending on the length of time that elapsed between preparation and analysis. Samples in acid solution which were allowed to stand always developed a yellow coloration n-hich became more intense on standing. It was therefore necessary to develop the procedures already described in order to obtain reproducible results. Although no detailed study was made of the amount of reduction for a given added excess of reducing agent, in general satisfactory results may be ob-
RECEITEDfor review October 14, 1955. Accepted August 4, 1956. Based on a dissertation submitted by Rudolph S. Bottei in partial fulfillment of the requirements for the degree of doctor of philosophy at Princeton University.
